Field of the Invention
This invention relates to processes and systems for treatment of groundwater or surface water that contains at least one of the following contaminants: nitrate, perchlorate, chromate, selenate, and volatile organic chemicals such as perchloroethylene, trichloroethylene, dichloroethylene, vinyl chloride, trichloropropanol, dibromochloropropane, and carbon tetrachloride. The new method implements a second treatment stage aerobic biofilter in combination with a first stage anoxic/anaerobic bioreactor with interstage oxygenation and particle conditioning addition.
Description of the Related Art
Raw drinking water sources may contain nitrate, perchlorate, chromate, selenate, and one or more of various volatile organic chemicals, for example, perchloroethylene, trichloroethylene, dichloroethlyene, vinyl chloride, trichloropropane, dibromochloropropane and carbon tetrachloride. There are numerous processes and technologies available for removing one or more of these contaminants from drinking water, including ion exchange, reverse osmosis, electrodialysis reversal, granular activated carbon adsorption, air stripping, and advanced oxidation. Each of these processes and technologies has one or more of the following disadvantages: exerts a high energy demand, exerts a high operational cost, generates of a high-strength concentrated waste stream that must be further treated or disposed, adds considerable salt to a given watershed, does not address all of the cited contaminants, is sensitive to raw water quality, and sensitive to operating conditions.
Various biological processes have also been tested and used to treat one or more of the cited contaminants. These processes are typically single stage biological reactors with upstream nutrient addition. These processes have one of more of the following disadvantages in that they: cannot treat all of the cited contaminants, produce excess biomass that can slough into the effluent of the bioreactor, can experience clogging due to the production of excessive extracellular polymeric substances, and can leak nutrients into the effluent, thereby causing biological regrowth potential and disinfection by-product formation potential.
Some processes may include an additional element with a particulate filter unit that may be sand, granular activated carbon, anthracite or similar media and may have a backwash system to reduce clogging and to fluidize the bioreactor bed. However, the filtration in these systems is for high rate particle filtration rather than for degrading and removing dissolved contaminants.